A new pathogenic fungus is threatening bats
An international team led by scientists from the University of Montpellier, in collaboration with scientists from the CNRS and partners in Germany, Bulgaria, Finland, and Ukraine, analyzed a massive number of samples of the fungus responsible for the largest mammal mortality event ever documented. This large-scale study, to which more than 360 volunteers contributed, was published in the prestigious journal Nature on May 28, 2025. It revolutionizes our current understanding of white-nose syndrome, revealing new insights into the identity and diversity of the pathogens involved.
Diseases don’t just affect humans: in 2006–2007, a massive and unexplained bat die-off was observed in a cave in New York State. The bats had a white powder on their snouts, caused by a then-unknown fungus, Pseudogymnoascus destructans. This fungal disease, known as “white-nose syndrome,” rapidly spread across North America, decimating hibernating populations with annual mortality rates exceeding 90% and causing the deaths of several million bats. Researchers discovered that this fungus originated in Eurasia, where it coexists with local bats without causing mass mortality. Its accidental introduction into North America triggered one of the most devastating epidemics ever documented in wild mammals.
For nearly 20 years, it was believed that the history of this pathogen was relatively straightforward: a single agent, a specific geographic origin (Europe), and well-established mechanisms. But new genetic data reveal a far more complex history, calling into question our assumptions about the origin, diversity, and evolutionary dynamics of this pathogenic fungus.
Not one, but two species of fungi cause the disease
Until recently, Pseudogymnoascus destructans was considered the sole causative agent of white-nose syndrome. However, this study, based on the analysis of an impressive number of samples (5,479) from 27 countries and three continents, highlights the existence of two distinct species of fungi capable of causing the disease, although only one of these species has been introduced into North America. This discovery challenges the notion of a single pathogen and reveals the complexity of the disease’s dynamics. It thus opens new perspectives on the evolution of virulence and on how these pathogens interact with their hosts depending on geographical contexts.
“We thought we knew our enemy, but we’re now discovering that it has two sides and is potentially more complex than we imagined, ” says Nicola Fischer, the study’s lead author, who completed her Ph.D. on the subject at the University of Greifswald in Germany and the University of Montpellier.
The discovery of a second pathogenic fungus—capable of causing white-nose syndrome and exhibiting different host specificity—poses a significant threat to bat conservation. Although the second species is currently absent from North America, its introduction could endanger bat species that have not yet been affected by the first. Furthermore, even bat species that are beginning to recover from exposure to the first pathogen could face new challenges if the second were to spread. This situation echoes the example of chytrid fungi that have devastated amphibian populations, where the emergence of a second, more specialized species following an initial generalist species had devastating effects. In the case of the second species of P. destructans, it is still possible to take preventive action to strengthen global biosecurity and limit the risks associated with this new threat.
The origin of its introduction to North America has finally been clarified
In Eurasia, both species of fungus are already present, but fungal populations there are highly geographically segregated. The main risk lies in the convergence—often driven by human activities—of previously isolated populations. This could promote genetic recombination within a single species, a mechanism well known in fungi for generating new variants, some of which may be more virulent. Such an emergence would pose a serious threat to Eurasian bats, even though they do not appear to have been affected so far.
Based on genetic analysis of more than 5,400 samples collected across Eurasia and North America, the study identifies for the first time the exact region of origin of the lineage responsible for the North American outbreak of white-nose syndrome: the Podillia region of Ukraine. This area, home to some of the world’s largest cave systems, has been a popular destination for international cavers—particularly those from North America—since the end of the Soviet Union. The results suggest that the accidental introduction of the fungus into North America—likely via exchanges with cave explorers from New York State, where the disease was first detected—stemmed from a single event. This study puts an end to nearly two decades of speculation about the origin of white-nose syndrome across the Atlantic and strikingly illustrates the impact that a single translocation event can have on wildlife.
Caving and biosecurity: a critical issue for disease prevention
This discovery highlights the significant risks that caving activities pose for the spread of pathogens and underscores the urgent need for a better understanding of “biological contamination” linked to human travel. Preventing the unintentional transport of pathogenic fungi such as Pseudogymnoascus destructans must become a priority in conservation and public health strategies, for both wildlife and humans. The systematic and thorough cleaning of caving equipment during travel is an essential measure: studies show that it drastically reduces the presence of viable spores and thus limits the spread of the fungus that causes white-nose syndrome.
This study would not have been possible without an extraordinary effort. Thanks to a collective data-collection effort spanning the Northern Hemisphere, involving several hundred volunteers—mostly chiropterologists—the researchers were able to analyze an exceptional dataset.
“This project demonstrates the power of citizen science. Well-trained volunteers, working within the right network, can help generate data of exceptional quality on a scale that would otherwise be impossible to achieve,”concludes Sébastien Puechmaille, study coordinator atthe Institute of Evolutionary Sciences in Montpellier(ISEM).